That's a tang, really cool coloration, it could be an aberrant. If so, it's incredibly rare!
It appears to be mimicking that coral in the background to me.
He had this patterning before he went in my display
Ok i wasnt really fussed with a species id i know what it is, i just thaught it a strange color variant, one i hadnt seen before and was wondering how common this Color varient is in the hobby...